There are a hundred examples of variable spellings in One Piece due to there being so many iterations and translators, so just my opinion, due to nostalgia and familiarity, I simply prefer "paramecia" over "paramythia." Everyone has personal preferences in all those examples. Funnily enough, I have no preference between Enel and Eneru, but it hurts to remember that the manga spells Zoro "Zolo" and Gan Fall "Ganfor."